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Supernovae source Astronomers have found the "smoking gun" that proves supernovae are a source of extremely high-energy cosmic rays.

A four-year research program involving scores of scientists, led by Dr Stefan Funk from Stanford University in California, shows cosmic-ray protons within our galaxy are accelerated in supernovae remnants, the leftovers of giant stars that have blown themselves apart.

"We've long suspected a link between cosmic rays and supernovae remnants, but this is the first proof," says Funk.

"Because they're charged particles, cosmic rays can be easily deflected by magnetic fields on their way from their source to Earth, so they arrive here with equal flux [quantities] from all directions."

"That's prevented us from discovering their point of origin."

Gamma ray photons

To overcome this, Funk and colleagues looked for high-energy, gamma-ray photons emitted by cosmic ray atomic nuclei. These are protons which have been accelerated to close to the speed of light by shockwaves produced by the expanding supernova remnant.

Using the Fermi Gamma-ray Space Telescope, Funk and colleagues focused on two of the brightest supernova remnants in our galaxy called IC 443 and W44.

IC 443 is roughly 5,000 light years away in the constellation Gemini, while W44 is located about 10,000 light years away, in the constellation of Aquila.

Writing in the journal Science, Funk and colleagues say they detected the characteristic signature of gamma-rays produced by pion decay, which is direct evidence of the acceleration of protons into cosmic rays by supernovae remnants.